1. Field of the Invention
This invention relates to an improvement applicable to an encoder. More specifically, this invention relates to an improvement applicable to a plurality of means for correction of offset, difference in amplitude and/or difference in phase which may occur in output signals of an optical encoder.
2. Description of the Related Art
Referring to FIG. 1, an exemplary means available in the prior art for correction of offset, difference in amplitude and/or difference in phase existing in output signals of an optical encoder.
The upper half of FIG. 1 illustrates an A phase encoder, and the lower half of FIG. 1 illustrates a B phase encoder. The A phase encoder and the B phase encoder are substantially identical to each other, excepting each of them has a function to individually detect the angular position of two independent parts of a single rotator, the angular position of the two independent parts differring from each other by 90 degrees in terms of phase.
A first means for sensing angular position of A phase (1A) detects the inverse phase of the phase which a second means for sensing angular position of A phase (2A) detects. The output signals of these two means (1A) and (1B) are input to a sine wave generator means of A phase (3A), which subtracts the one of the two signals from the other of the two signals and generates a sine wave signal which represents the angular position of the rotator. If the sine wave generator means of A phase (3A) happens to generate a sine wave signal containing an offset caused by a difference in amplitude existing between the output signal of the first means for sensing angular position (1A) and the output signal of the second means for sensing angular position (2A), an operational amplifier for erasing offset of A phase (31A) is employed for the purpose to erase the offset existing in the output signal of the A phase encoder. In other words, an adjuster means e.g. a volume resistor of the operational amplifier for erasing offset of A phase (31A) is adjusted to adjust the amplification factor of the operational amplifier for erasing offset of A phase (31A), resultantly causing the amplitude of the output signal of the first means for sensing angular position of A phase (1A) to become equal to the amplitude of the output signal of the second means for sensing angular position of A phase (2A).
Similar operation is conducted also for the B phase encoder which detects the angular position of a part whose angular position differs from that of the part of the same rotator whose angular position is detected by the A phase encoder, by 90 degrees in terms of phase. In other words, the output signals of a first means for sensing angular position of B phase (1B) and the output signals of a second means for sensing angular position of B phase (2B) are input to a sine wave generator means of B phase (3B), which subtracts the one of the two signals from the other of the two signals and generates a sine wave signal which represents the angular position of the rotator. If the sine wave generator means of B phase (3B) happens to generate a sine wave signal containing an offset caused by a difference in amplitude existing between the output signal of the first means for sensing angular position (1B) and the output signal of the second means for sensing angular position (2B), an operational amplifier for erasing offset of B phase (31B) is employed for the purpose to erase the offset existing in the output signal of the B phase encoder. In other words, an adjuster means e.g. a volume resister of the operational amplifier for erasing offset of B phase (31B) is adjusted to adjust the amplification factor of the operational amplifier for erasing offset of B phase (31B), resultantly causing the amplitude of the output signal of the first means for sensing angular position of B phase (1B) to become equal to the amplitude of the output signal of the second means for sensing angular position of B phase (2B).
If a difference in amplitude happens to exist between the output signal of the sine wave generator means of A phase (3A) and the output signal of the sine wave generator means of B phase (3B), an operational amplifier for erasing amplitude difference of A phase (32A) which is attached to the sine wave generator means of A phase (3A) or an operational amplifier for erasing amplitude difference of B phase (32B) which is attached to the sine wave generator means of B phase (3B) is employed for the purpose to make the amplitude of the sine wave output of the sine wave generator means of A phase (3A) equal to the amplitude of the sine wave output of the sine wave generator means of B phase (3B). In other words, an adjuster means e.g. a volume resistor of the foregoing operational amplifier (32A) or (32B) is adjusted to adjust the amplification factor of the foregoing operational amplifier (32A) or (32B), resultantly satisfying the above purpose.
If the difference in phase between the sine wave output signal of the sine wave generator means of A phase (3A) and the sine wave output signal of the sine wave generator means of B phase (3B) happens to differ from 90 degrees, either an operational amplifier for erasing phase difference error of A phase (33A) or an operational amplifier for erasing phase difference error of B phase (33B) is employed for the purpose to erase the error in phase difference. In other words, the output signal of either the operational amplifier for erasing phase difference error of A phase (33A) or the operational amplifier for erasing phase difference error of B phase (33B) is added to or subtracted from the output signal of the sine wave generator means of the other phase (3B) or (3A) respectively, to shift the phase, resultantly to erase the error in phase difference. In this case, adjustment of the output signal of the operational amplifier for erasing phase difference error of A phase (33A) or adjustment of the output signal of the operational amplifier for erasing phase difference error of B phase (33B) is generally conducted by adjusting the amplification factor respectively of the operational amplifier for erasing phase difference error of A phase (33A) or of the operational amplifier for erasing phase difference error of B phase (33B). The adjustment of the amplification factor is conducted by employing an adjuster means e.g. a volume resistor of the operational amplifier for erasing phase difference error of A phase (33A) or by employing an adjuster means e.g. a volume resistor of the operational amplifier for erasing phase difference error of B phase (33B).
The above description explains an optical encoder available in the prior art and which is employable for detecting the angular position of a rotator and which is designed to erase or correct various errors. The prior art embodiment corrects errors including a difference in amplitude which happens to exist between two signals which represent the angular position of the foregoing rotator and which have a difference in phase by 180 degrees or 90 degrees between each other, an error which happens to exist for the difference in phase which theoretically should be 90 degrees or 180 degrees, and/or an offset which happens to exist for the one or both signals described above. However, the correction of such errors is accomplished by adjusting the amplification factor of one or more operational amplifiers, such adjustment being conducted by adjusting one or more adjuster means e.g. one or more volume resistors attached to the foregoing one or more operational amplifiers. Since the foregoing adjustment is troublesome and requires a long time to conduct, and since the foregoing operational amplifiers accompanied by adjuster means, e.g. one or more volume resistors, requires a large space for installation, the optical encoder available in the prior art suffers drawbacks which are desirable to remove.